1. Field of the Invention
The present invention generally relates to an interface circuit between a semiconductor element circuit and a Josephson junction element circuit, and more particularly an interface circuit for correctly transferring a signal from a semiconductor element circuit including semiconductor elements to a Josephson junction element circuit including Josephson junction elements.
2. Description of the Prior Art
Josephson junction elements operate at high speed and consume little power. Hence, a high-speed processor can be made using Josephson junction elements. Conventionally, in the experiments for testing the operation of a Josephson junction element circuit, a signal pattern for testing the Josephson junction element circuit is generated by a signal generator formed with a semiconductor circuit and is applied thereto.
A Josephson junction logic gate is biased by an alternating current signal for a latching operation, and is reset every clock. A semiconductor logic gate including transistors made of, for example, silicon, is biased by a direct current signal, and is not reset every clock. Further, Josephson elements are required to be operated in synchronism with a clock signal having a frequency higher than that of a clock signal with which semiconductor elements are synchronized. Hence, if a signal from the semiconductor element circuit is directly applied to the Josephson junction element circuit, identical data from the semiconductor element will be received by the Josephson junction element circuit many times within the same cycle of the clock signal for the semiconductor element circuit. Hence, the Josephson junction element circuit malfunctions.
With the above in mind, an interface circuit has been proposed in which a single Josephson junction element is included. When the level of a signal from the semiconductor element circuit exceeds a threshold level, the resistance of the Josephson junction element changes from zero ohms to a certain value. However, the above conventional interface circuit needs to establish synchronization between the semiconductor circuit and the Josephson circuit. That is, the operation of the Josephson circuit must be synchronized with the operation of the semiconductor circuit. The circuit arrangement for establishing the synchronization is very complex, and degrades the high performance of Josephson junction elements.